Many types of dialing systems are known in which a group of telephone numbers can be stored and, upon manual selection, a particular number is transmitted over a telephone line to a central station to provide a transmission linkage between the calling station and the selected called station. One well known dialing system employs a tape or belt mounted for forward and backward motion by a suitable transport mechanism. Magnetic or optically coded signals are recorded across the width of the magnetic tape to represent each stored telephone number. To dial a particular number, the tape is moved to an index position where the stored number is in registration with a read head which scans across the width of the tape to decode the data content thereof and cause dialing information to be transmitted to effect the connection to a called station. See, for example, U.S. Pat. No. 3,757,054. In another known telephone dialer, information is stored in the form of perforations on cards which can be selectively inserted into a card-reading mechanism to dial the number encoded on the card. In still other known telephone dialers, a manual, mechanically alterable memory is comprised of interwired switches or matrix crossings such that a telephone number is stored by predetermined switch settings or matrix linkages and a particular telephone number is read out by activating a selector switch corresponding to the switches or matrix containing the stored number. See, for example, U.S. Pat. No. 3,555,201 and 3,665,113. These dialing systems are all rather mechanically complex to manufacture, operate and maintain, and relatively expensive.
Specialized electronic circuits have been proposed for use in conjunction with telephone numbers stored in a random access memory but such circuits have generally been rather limited because they require separate buttons to address each telephone number stored in addition to a 0-9 digit keyboard for entry of telephone numbers to be stored. See, for example, U.S. Pat. No. 3,735,050. It is desirable to have a simple dialing system which is adapted to efficiently and easily store a desired repertoire of telephone numbers.
It is therefore an object of the present invention to provide a simple and relatively inexpensive automatic dial system for a subscriber telephone set which has the capability of storing a group of telephone numbers and which performs automatic dialing of the stored telephone numbers.
Another object of the invention is to provide an easily expandable automatic dial system for a subscriber telephone utilizing a randomly accessed electronic memory.
A further object of the invention is to provide an automatic dial system for a subscriber telephone which requires only a single numeric keyboard array for storing telephone numbers, manually dialing telephone numbers and selectively retrieving telephone numbers from a memory for automatic dialing.
It is still another object of the invention to provide a replacement telephone dial capable of being mounted in any standard telephone set without altering the existing physical structure to provide the telephone set with automatic dialing capability.